鎢表面上單原子與原子團動態之研究

Abstract

本研究中，我們利用場離子顯微鏡觀察銥吸附原子、鎢原子團、及鎢台階邊緣原子在鎢表面的擴散運動。實驗結果得到銥吸附原子在W(211)、W(110)、W(111)平台上的擴散活化能分別為0.66±0.03eV、0.95±0.04eV、1.56±0.01eV；而銥吸附原子在W(111)平台邊緣的擴散活化能則約為1.41±0.1eV。 鎢原子團在W(111)平台上的擴散模式主要有兩種類型：一種為基本的單一原子跳躍模式，另一種則為邊緣原子整排的滑動模式，而根據實驗研究的結果顯示，此兩種模式是並行產生的；鎢原子團的擴散活化能會隨著原子團的增多而有振盪和增加的趨勢；我們也觀察到鎢原子團在W(111)切面上所呈現的多樣化形貌，而且原子團以二維方式的排列會較一維方式排列穩定；不論原子個數為多少的原子團，其形貌以緊密狀結構出現的機會也會較直鏈狀結構頻繁。當三、六顆原子團在呈現正三角形的形貌時，會較其他種形貌穩定而難以改變其結構。 最後我們針對W(111)切面上平台邊緣原子的擴散行為進行研究，並將各種動態行為的發生做溫度上的定位；由於W(111)是呈現三對稱的切面，若平台是以三對稱的形貌出現或是沒有邊緣原子的存在，會較為穩定不易發生形貌上的轉變。

In this study, the diffusion dynamics of individual Ir adatoms, W clusters, and W edge atoms on the W surfaces has been investigated by field ion microscopy. The activation barriers for the terrace diffusion of Ir adatoms on W(211), (110) and (111) surfaces are determined to be 0.66±0.03eV、0.95±0.04eV、1.56±0.01eV, respectively. The activation barrier of Ir adatoms diffusion along the W(111) edges is about 1.41±0.1eV. There are two major types for W clusters diffusion on W(111)；One type is the atomic hopping of singular atoms, the other type is the edge sliding of whole atom lines. From the analysis of appearance probability the two types are equal. The activation energy of W clusters diffusion on W(111) surfaces as a function of cluster size has oscillatory and increasing behaviors. We observe the various shapes of W clusters and find that the two-dimensional W clusters on W(111) surfaces are more stable than one-dimensional clusters. No matter what the number of atoms in the clusters is the close compacted configurations are observed more frequently than the chain configurations. When trimer and hexamer show the equilateral triangle shapes, they will be more stable than other kinds of shapes. Finally, we investigate into the behavior of the edge atoms of W clusters on W(111) surfaces. We locate the occurrences of the different dynamic behaviors on the temperature scale. Because the W(111) surface isa three symmetrical plane, the terrace with three symmetrical shapes or without edge atoms is more stable and changed its shape difficultly.